Internal parasites in dogs

Sep 2, 2022

Dogs are our best friends, and we live with them in our daily lives. They are playful, affectionate animals and give us all their love. It is our responsibility to take care of them and provide them with everything that is necessary to guarantee their well-being. Among these obligations is the importance of correctly carrying out deworming – both external and internal – to safeguard their health, and ours.

What are internal parasites?

Previously in this blog we talked about external parasites that can affect dogs, such as fleas, ticks, or mosquitoes, however, today we want to talk about internal parasites.

These are a type of parasite that can infest dogs and cause serious health problems if they are not treated properly. Most of these parasites affect the digestive system, but there are also the protozoa that cause leishmaniasis or the worms that cause dirofilariasis, or heartworm.

Parasites that affect the digestive system are usually located in the intestine, where they feed by sucking blood and nutrients. They can cause tissue damage, anemia, an intestinal obstruction, or in the worst cases, death.

Types of internal parasites

There are several types of internal parasites in dogs, of different shapes, lengths and there are even some that affect dogs at a certain age, such as puppies, but not adults.

Nematodes or roundworms

Roundworms or intestinal worms in dogs are usually more frequent in puppies. The best known are the roundworms (toxocara canis and toxascaris leonina) and they usually live in the stomach and intestines. This parasite usually grows quite large resulting in being very unpleasant.

Puppies are infected with this parasite through the female, in the uterus during pregnancy, or once they are born through the ingestion of mother’s milk.

Young dogs can become infected by ingesting an infected animal, such as a rodent, so city domestic dogs are unlikely to become infected. Another way is through the feces of another infested animal, or the ingestion of larvae in contaminated environments.

The dogs most exposed to this type of parasite are those that live in the countryside, so it is very important to be alert if you have a puppy and live outside the city.


This parasite is a small larva about 2mm long that attaches itself to the dog’s small intestine, feeding on its blood.

They can be spread from mother to puppy, by ingestion of worm larvae, they can also pass through the dog’s skin directly, or after ingestion of an affected host.

These worms can become very dangerous, especially in puppies because, even though they are small, they feed on the animal’s blood, causing anemia.

Tapeworms or flatworms

It is a worm that also lives in the small intestine of the dog and looks like small grains of rice, and can be shown alone or in a chain, which can be up to 2m long. Although it is an extremely long parasite that should not live inside a dog, it is often very difficult to detect because it does not cause obvious symptoms in their health.

This parasite is not transmitted between dogs, but through an external intermediary agent such as fleas, small rodents, raw fish, or butchery offal. For this reason, it is important to maintain control of both external and internal parasites of the animal since, in this case, they may be linked.

When the animal eats an intermediate host, it later develops the definitive roundworm. The eggs are small and spread easily by the wind, they can be found on berries, mushrooms, vegetables, or the dog’s fur. The worm does not usually cause symptoms in the infected dog and is transmitted through infected animals, such as raw viscera, so it is essential not to give the dog raw food as it can subject it to the risk of tapeworms.

This type of intestinal parasites can also affect humans through serious diseases such as hydatid disease, so it is very important to keep them under control.

Giardia and coccidia in dogs

These are small parasites that infect the dog’s intestinal mucosa and can cause diarrhea in the animal. These are flagellated protozoa, and can affect dogs, humans, and other animals.

The most common way for dogs to get infected is by eating the feces of another affected animal or drinking contaminated water.

The symptoms are not always obvious, in fact, there are dogs that do not even show them, but if they do, they are usually diarrhea, bloody diarrhea, abdominal swelling or weight loss.

While giardia is highly contagious and difficult to expel from the environment, coccidia are relatively easy to treat.


It is a worm that affects the heart, more specifically the right ventricle and atrium, as well as the pulmonary artery. They are transmitted by mosquitoes, especially those that live in tropical or temperate countries.

How to know if a dog is infested?

There are many types of internal parasites that can affect dogs, however, except for some specific cases, there are usually quite clear symptoms that indicate the need to go to the vet to receive advice on the most appropriate treatment.

The most common symptoms that we detect from an infested dog are:

  1. Diarrhea
  2. Bloody feces
  3. Vomiting
  4. Abdominal pain and swelling
  5. Cough or in some cases respiratory problems
  6. Weight loss
  7. Lack of appetite
  8. Anemia (in cases of heavy blood loss)
  9. Intestinal obstruction: in cases where the worms form a ball and cannot be expelled

Treatment against intestinal parasites

The best treatment against any parasite is prevention. For this, the basics are to be careful with what the dog ingests, especially if it eats feces from other animals or contaminated water. It is also important to carry out regular deworming with veterinary advice.

However, if we are facing a case of intestinal parasite infestation, the veterinarian should start an internal antiparasitic treatment.

For this there are medicines for intestinal parasites in the form of pills or tablets. Most of these medications do not require a prescription, however it is always good for it to be carried out under expert supervision.

In conclusion…

There are many types of parasites that can affect your dog internally, some are more aggressive than others, and some can even affect other members of the family.

For this reason, it is essential to keep your dog’s periodic deworming at bay to avoid infestations that could compromise the health of the animal or other members of the family. In the case of suspecting that the dog may be infested, it is important to go to the veterinarian as soon as possible before the problem worsens.